Automatic pressure regulator for vacuum discharge tubes



Oct. 2, 1934. M, N. STATES 1,975,561

AUTOMATIC PRESSURE REGULATOR FOR VACUUM DISCHARGE TUBES Filed Feb. 1, 1932 Mars/lad M 522325 Patentcl Oct. I 2, 1934 AUTOMATIC PRESSURE REGULATOR FOR VACUUM DISCHARGE TUBES Marshall N. States, Evanston, Ill;', assignor to Central Scientific Company, 'a corporation of Illinois Application February" 1,

22 Claims.

The beautiful phenomena attendingthe discharge between well spaced electrodes as the air pressure in the surrounding space is reduced can beobtained by connecting a static machine, or induction coil, across electrodes in the respec tive ends of a long discharge tube and connecting the interior of the tube with a modernyacuum pumping outfit. v

When the pressure within the tube is atv or near atmospheric no discharge will pass between the electrodes, nor will the air become visibly conducting until the pressure is very much reduced. At about one-sixth of an atmosphere (10 to 15 centimeters of mercury)- bluish threads of light will trickle alongthe walls of the tube accompanied by a crackling sound, but it will be difiicult to tell the anode from the cathode.

As the pressure is lowered the threads of light will thicken and appear to travel mostly through the.- air until, at length, a vivid red glow will fill the central cross sectional part of the tube from the anode to a faintly lighted area near the cathode, which area marks the beginning of the Faraday dark space, so called.

The red glow, called the positive column,. will develop into distinct disks of red glow spaced by minute dark disks. The Faraday dark space will expand and travel toward the anode followed by a light known as the cathode glow, which.

extends from a velvet glow on the cathode. The positive column all but recedes into theanode and a fluorescent glow spreads over the walls of the tube. The electric resistance which has decreased with the air pressure will now begin to rise, the colors will fade, and the visible phenomena end as the vacuum becomes, hard. T

The transition of the phenomena is more rapid than even this sketchy description indicates, and the entire period is much too brief for either scientific study or entertainment. Repetition is necessary, and it has heretofore been effected by manually letting the vacuum down, which ever included the human errors, distracted the students, or the customers, or the observers, and in many appropriate uses of the apparatus has added the prohibitive cost of an attendant. r

The principal objectof this invention is to effect automatic repetition of the phenomena at selected intervals, thereby increasing their pedagogical value and renderingtheir attractiveness available for entertainment and advertising.

Further objects and advantages of this invention will be revealed as the disclosure proceeds and the description is read in connection with the accompanying drawing, in which 1932, Serial No. 590,068

Fig. 1 is a diagram of a selected discharge tube vacuum pump and induction coil connected to produce the phenomena described, and with an attachment made according to this invention for automatically letting down the vacuum when it becomes hard and thereby initiating a repetition of the cycle of operations;

Fig. 2 is similar to a part of Fig. 1, showing a modification, and

Fig. 3 is an enlarged sectional view of a fragment illustrating how the mercury adheres by surface tension to the bottom of the column at one stage of the operation.

But the drawing and the specific description that follows are used to disclose and illustrate the invention and not to define its scope.

The vacuum discharge tube 10 is made of soda glass, 5 feet long, 2 inches in diameter, and

equipped with flat aluminum disk electrodes 11 At one side of the' and 12, 2 inches in diameter. tube and at the approximate longitudinal center a tubular arm 13, of an inch in diameter, is provided for establishing communication with the interior.

The electrodes 11 and 12 are connected with an induction coil 14 yielding not less than a 3 inch spark. (The effect may be intensified by using a high tension transformer.) The arm 13 is connected by special vacuum tubing 16 and vacuum wax or stop-cock grease with what may be called, for convenience, a low pressure tube 1'7 having a lateral arm 18 connected in like manner with a vacuum pump 19, driven by a motor 20. The motor circuit and the electric discharge circuit are controlled by a single switch 21.

The low pressure tube 17 is enlarged at 22 to form a bulb receiving the curved discharge tube 23 extending upwardly and lateral-1y from the top of a mercury column 24 (mercury is here used to include all those well known equivalent liquids, though metallic mercury is preferred because it permits the apparatus to be made in more convenient size.) Below the bulb 22 the low pressure tube 17 resumes its normal size for a distance indicated at 25, and then is reduced to a capillary 1 0 tube 26, which is return-bent at 2'7 and joined to the bottom of what is, for convenience, called a high pressure tube 28, surrounding the column 24 up to about the line marked B, and afiording somewhat of a vessel below the line marked C. The high pressure tube 28 has an upwardly inclined arm 29, which is intermediately connected by a construction 30 with a high pressure bulb 31. having an arm 32 connected with a volume chamber 33, by extending through the stopper 34. The no stopper also carries an L-shaped tube 35 equipped with a rubber tube 36, a pinch cock 3'7, and a capillary tube 38, which communicates with the atmosphere or a cylinder of the gas to be studied.

The low pressure tube 1'7 is made of soda glass inch in diameter and the arm 18 is the same diameter. The capillary tube 26 is inch inside diameter; the mercury column24 is inch in diameter, and 4 inches long between the lines B and C. The high pressure tube 28 is inch in diameter, and is arranged as closely to the low pressure tube 17 as is convenient in manufacture. The arm 29, the bulb 31 and the arm 32, and the construction 30 are about in the proportion shown. The volume chamber 33 is a 12 litre flask. The tube 35 is A inch in diameter and the capillary 38 is inchinside diameter and 12 inches long. When the apparatus used has these dimensions, the vacuum pump should be of such capacity that it reduces the pressure in the discharge tube from about 2 inches of mercury to a hard vacuum in about 3 minutes.

Operation Before starting the mercury should be at the level D with atmospheric pressure in the tubes 17 and 28.

By closing the switch 21 to the position shown in Fig. 1, the motor 20 and the sparking apparatus are energized. Almost immediately the mercury I will rise in the low pressure tube to the line A,

and there will be a corresponding drop in the high pressure tube 28. The mercury will gradually rise in the column 24 to the line B, when the relation at the bottom of the column will be substantially as illustrated in Fig. 3.

A little additional pressure differential between the tubes 17 and 28, and the surface tension of the mercury at 39, Fig. 3, will be overcome. Air will enter the bottom of the column 24 and the mercury will rise through the arm 23 and pour into the bulb 22, from which it will run down through the capillary tube 26 and replenish the bottom of the tube 28, with the result that there will be a mixed column of air and mercury rising through the column 24 until the pressure in the tube 17 is brought down to about 2 inches of mercury, when the mercury at the bottom of the column 24 will again seal it against the admission of air from the tube 28.

The phenomena described at the beginning of this specification will then take place and when the vacuum becomes hard the pressure difierential between the tubes 17 and 28 will again cause the mercury in the column 24 to be discharged and air will be admitted to the system to let the vacuum down and set the apparatus for another cycle of operations.

The tube 1'7 just above the bulb 22 is provided with an interior nipple 40 bent to the side, as indicated in Fig. 1, to prevent gas rushing upwardly from entraining mercury and carrying it into the arm 18 leading to the pump or to the discharge tube 10.

The apparatus just described will repeat the cycle of operations at three minute intervals, or over, depending upon the constriction of tube 36 by the pinch cock 3'7.

Shorter intervals may be had by reducing the size of the flask 33. Of course this could also be accomplished by changing the proportion of other parts, the size of speed of the pump, etc.

When the apparatus is stopped for any considerable period, there may be suflicient leaks on the low pressure side of the air column to reverse the difierential and in consequence the flow. The bulb 31 will then act as a mercury trap and prevent escape to the flask 33. V

In the modified form shown in Fig. 2, the low pressure tube 41, instead of enclosing the mercury column 24 is arranged along side it. This construction is not as sturdy as that shown in Fig. 1, nor is it as easy to efiect the making or breaking of the mercury seal at the bottom of the column. It will, however, serve to illustrate a variant form.

The colors seen in the phenomena of the discharge tube may be varied by selecting the gas within it and the glass of which the tube is made. In nitrogen all the glow about the cathode is bright violet and the remaining color is rosy; in hydrogen blue is the dominant color, unless the tube is reduced at some area, in which case crimson would show; in carbon dioxide the light is remarkably white. Soda glass contributes to green fluorescence while lead and pyrex glasses contribute to blue.

I claim as my invention:-

1. In apparatus of the class described, comprising a vacuum discharge tube having electrodes, means for furnishing a high voltage discharge connected across the electrodes, and a vacuum pump connected with the interior of the tube in combination with automatic valve means for letting the vacuum down a substantial amount each time it becomes hard, and for allowing the vacuum pump to increase the vacuum again to the hard stage after each let-down.

2. In apparatus of the class described, comprising a. vacuum discharge tube having electrodes, means for furnishing a high voltage discharge connected across the electrodes, and a vacuum pump connected with the interior of the tube in combination with automatic means adapted to let the vacuum down a substantial amount each time it becomes hard, and to allow the vacuum pump to increase the vacuum again to the hard stage after each let-down, comprising a column of mercury subject to the vacuum in the tube above and a higher pressure below.

3. In apparatus of the class described, comprising a vacuum discharge tube having electrodes, means for furnishing a high voltage discharge connected across the electrodes, and a vacuum pump connected with the interior of the tube in combination with automatic means for letting the vacuum down when it becomes hard. comprising a volume chamber having a slow leak to the atmosphere and a column of mercury subject above to the vacuum in the tube and below to the pressure in the volume chamber.

4. In apparatus of the class described, comprising a vacuum discharge tube having electrodes, means for furnishing a high voltage discharge connected across the electrodes, and a vacuum pump connected with the interior of the tube in combination with automatic means for letting the vacuum down when it becomes hard. comprising a column of mercury subject to the vacuum in the tube above and a higher pressure below, and means to conduct mercury from the top to the bottom of the column.

5. In apparatus of the class described, comprising a vacuum discharge tube having electrodes, means for furnishing a high voltage discharge connected across the electrodess, and a vacuum pump connected with the interior of the tube in combination with automatic means for letting the vacuum down when it becomes hard, QOmprising a column of mercury subject to the the sealed tube, a high-pressure chamber, a disvacuum in the tube above and a higher pressure below, and means to conduct mercury from the top to the bottom of the column, including a capillary tube.

6. An article of manufacture for automatically letting down the vacuum in a discharge tube comprising as a unitary structure a column adapted to receive mercury, a high pressure tube in suitable communication with the bottom of the col umn, a low pressure tube in communication with the top of the column, and adapted to be connected with the interior of the vacuum discharge tube, and a return tube between the low pressure tube and the bottom of the column for returning mercury discharged from the top of the column, the low pressure tube between the return tube and the connection with the top of the column being unobstructed.

7. An article of manufacture for automatically letting down the vacuum in a discharge tube comprising as a unitary structure a column adapted to receive mercury, a high pressure tube in suitable communication with the bottom of the column, a low pressure tube in communication with the top of the column. and adapted to be connected with the interior of the vacuum discharge tube, and a return tube between the low pressure tube and the bottom of the column for returning mercury discharged from the top of the column, the high pressure tube enclosing the lower portion of the column, and the low pressure tube between the return tube and the connection with the top of the column being unobstructed.

3. An apparatus for periodically varying the vacuum in a sealed tube, comprising in combination, a vacuum pump 0 acted to exhaust the sealed tube, a vertical lowssure tube connected at its top with the scale. tube by a passage and having an enlarged portion, a shield above the enlarged portion adapted to allow downward passage of any fluid but to prevent liquid from being thrown up into the top portion of the low-pressure tube, a high-pressure chamber, a discharge tube communicating at one end with the enlarged portion of the low-pressure tube, and having its other open end extending downward into said high-pressure chamber, and a capillary return passage from the bottom of the low-pressure tube to the high-pressure chamber which passes at some point below the level of the high-pressure end of said discharge tube, the highepressure chamber being adapted to retain a liquid at a level above the opening of the discharge tube and to be connected to a closed vessel provided with an adjustable slow leak through which the desired gas may be made to flow.

9. in an apparatus for periodically varying the vacuum in a sealed tube, a vacuum pump con-= nected to exhaust the sealed tube, a low-pressure chamber connected by a passage at its top with charge tube open at both ends, entering the lowpressure chamber, and having its other end extending downward into the high-pressure chambar, a return passage from the bottom of the low-pressure chamber to the high-pressurechamher which passes at some point below the level of the high-pressure end of the discharge tube, and a closed gas reservoir having communication with the high-pressure chamber, and having an ad justable slow leak through which the desired gas may be made to flow.

10. A periodically-acting vacuum-release valve adapted to be connected between an electrical discharge tube which is continually being exhausted and a partially-exhausted gas chamber into which the gas desired is slowly admitted, comprising a low-pressure chamber, a discharge tube communicating at one end with the lowpressure chamber, a high-pressure chamber communicating with the other end of the discharge tube and connected with a passage adapted to be led into the partially exhausted gas chamber,

" and a return tube leading from the bottom of the ing an enlargement below said means, a discharge tube having its lower end open and extending down and its upper and bent over and leading into the low-pressure tube, a high pressure tube surrounding the lower part of the discharge tube and providing a space both above and below the level of the lower end of the discharge tube adapted to hold a liquid, a. capillary return tube leading from the lower end of the low-pressure tube to the high-pressure tube and having a portion below the level of the high-pressure tube, and a passage entering the high-pressure tube, having a trap to return a liquid to the high-pressure tube, and adapted to be led into said partially exhausted gas chamber.

12. An apparatus for periodically making hard and letting down the vacuum in an electrical discharge tube, comprising in combination, a vacuum pump connected to exhaust the electrical discharge tube, a low-pressure chamber, a passage having one end opening into the low-pressure chamber, a high-pressure chamber into which the other end of the passage opens, providing space both above and below the level of the opening of said passage thereinto for the retention of a liquid, and another passage adapted to allow a liquid to be retained in the high-pressure chamber, for providing communication between the high-pressure chamber and a partially exhausted vessel into which the desired gas is slowly admitted.

13. In an apparatus for periodically making hard and letting down the vacuum in an electrical discharge tube, a vacuum pump connected to ex haust the electrical discharge tube, high and low pressure chambers, a discharge tube providing communication between the chambers, and a return tube leading from the bottom of the low-pressure chamber to the high-pressure chamber and passing at some point below the level of the opening of the discharge tube into the highpressure chamber, said high-pressure chamber providing space both above and below the level of the opening or the discharge tube thereinto for retaining a liquid, and communicating with a passage adapted to allow the retention of a liquid in the high-pressure chamber, for connecting the high-pressure chamber with the partially exhausted vessel into which the desired gas is slowly admitted.

it. The process of applying a high voltage across the electrodes in a discharge tube, con tinuously exhausting the gas from the discharge tube, releasing a substantially fixed quantity of 

